Today | News | Books | Recipes Adventure | Science Fiction | Ghost stories | Poetry | Children | History Bookde, and set thou there the
degree of the mone according with the egge of the label. Than
afterward awayte where is than the degree of the sonne, at that
tyme. Remeve thou than the label fro the mone, and bringe and
sette it iustly upon the degree of the sonne. And the point of 10
the label shal than declare to thee, at what houre of the day or of
the night shal be flode. And there also maist thou wite by the
same point of the label, whether it be, at that same tyme, flode or
ebbe, or half flode, or quarter flode, or ebbe, or half or quarter
ebbe; or ellis at what houre it was last, or shal be next by night or 15
by day, thou than shalt esely knowe, &c. Furthermore, if it so be
that thou happe to worke for this matere aboute the tyme of the
coniunccioun, bringe furthe the degree of the mone with the
labelle to that coste as it is before seyd. But than thou shalt
understonde that thou may not bringe furthe the label fro the 20
degree of the mone as thou dide before; for-why the sonne is
than in the same degree with the mone. And so thou may at that
tyme by the point of the labelle unremeved knowe the houre of
the flode or of the ebbe, as it is before seyd, &c. And evermore
as thou findest the mone passe fro the sonne, so remeve thou the 25
labelle than fro the degree of the mone, and bringe it to the
degree of the sonne. And worke thou than as thou dide before,
&c. Or elles knowe thou what houre it is that thou art inne, by
thyn instrument. Than bringe thou furth fro thennes the labelle
and ley it upon the degree of the mone, and therby may thou wite 30
also whan it was flode, or whan it wol be next, be it night or
day; &c.
[_The following sections are spurious; they are numbered so as to shew
what propositions they repeat._]
41_a_. UMBRA RECTA.
Yif thy rewle falle upon the 8 poynt on right schadwe, than make
thy figure of 8; than loke how moche space of feet is be-tween thee
and the tour, and multiplye that be 12, and whan thou hast multiplied
it, than divyde it be the same nombre of 8, and kepe the residue; and
adde therto up to thyn eye to the residue, and that shal be the verry 5
heyght of the tour. And thus mayst thou werke on the same wyse, fro
1 to 12.
41_b_. UMBRA RECTA.
An-other maner of werking upon the same syde. Loke upon which
poynt thy rewle falleth whan thou seest the top of the tour thorow two
litil holes; and mete than the space fro thy foot to the baas of the
tour; and right as the nombre of thy poynt hath him-self to 12, right
so the mesure be-tween thee and the tour hath him-self to the heighte 5
of the same tour. Ensample: I sette caas thy rewle falle upon 8;
than is 8 two-thrid partyes of 12; so the space is the two-thrid partyes
of the tour.
42_a_. UMBRA VERSA.
To knowe the heyghth by thy poyntes of _umbra versa_. Yif thy
rewle falle upon 3, whan thou seest the top of the tour, set a prikke
there-as thy foot stont; and go ner til thou mayst see the same top at
the poynt of 4, and sette ther another lyk prikke. Than mete how
many foot ben be-tween the two prikkes, and adde the lengthe up to 5
thyn eye ther-to; and that shal be the heyght of the tour. And note,
that 3 is [the] fourthe party of 12, and 4 is the thridde party of 12.
Now passeth 4 the nombre of 3 be the distaunce of 1; therfore the
same space, with thyn heyght to thyn eye, is the heyght of the tour.
And yif it so be that ther be 2 or 3 distaunce in the nombres, so
shulde 10
the mesures be-tween the prikkes be twyes or thryes the heyghte of
the tour.
43_a_. AD COGNOSCENDUM ALTITUDINEM ALICUIUS REI PER UMBRAM RECTAM.
To knowe the heyghte of thinges, yif thou mayst nat come to the
bas of a thing. Sette thy rewle upon what thou wilt, so that thou may
see the top of the thing thorw the two holes, and make a marke ther
thy foot standeth; and go neer or forther, til thou mayst see thorw
another poynt, and marke ther a-nother marke. And loke than what 5
is the differense be-twen the two poyntes in the scale; and right as
that difference hath him to 12, right so the space be-tween thee and
the two markes hath him to the heyghte of the thing. Ensample: I
set caas thou seest it thorw a poynt of 4; after, at the poynt of 3.
Now passeth the nombre of 4 the nombre of 3 be the difference of 1; 10
and right as this difference 1 hath him-self to 12, right so the mesure
be-tween the two markes hath him to the heyghte of the thing, putting
to the heyghte of thy-self to thyn eye; and thus mayst thou werke
fro 1 to 12.
42_b_. PER UMBRAM VERSAM.
Furthermore, yif thou wilt knowe in _umbra versa_, by the craft of
_umbra recta_, I suppose thou take the altitude at the poynt of 4, and
makest a marke; and thou goost neer til thou hast it at the poynt of
3, and than makest thou ther a-nother mark. Than muste thou
devyde 144 by eche of the poyntes be-fornseyd, as thus: yif thou 5
devyde 144 be 4, and the nombre that cometh ther-of schal be 36, and
yif thou devyde 144 be 3, and the nombre that cometh ther-of schal be
48, thanne loke what is the difference be-tween 36 and 48, and ther
shalt thou fynde 12; and right as 12 hath him to 12, right so the space
be-tween two prikkes hath him to the altitude of the thing. 10
COMMENTARY ("FOOTNOTES").
Little Lewis my son, I perceive that thou wouldst learn the Conclusions of
the Astrolabe; wherefore I have given thee an instrument constructed for
the latitude of Oxford, and purpose to teach thee _some_ of these
conclusions. I say _some_, for three reasons; (1) because some of them are
unknown in this land; (2) because some are uncertain; or else (3) are too
hard. This treatise, divided into five parts, I write for thee in English,
just as Greeks, Arabians, Jews, and Romans were accustomed to write such
things in their own tongue. I pray all to excuse my shortcomings; and thou,
Lewis, shouldst thank me if I teach thee as much in English as most common
treatises can do in Latin. I have done no more than compile from old
writers on the subject, and I have translated it into English solely for
thine instruction; and with this sword shall I slay envy.
The _first_ part gives a description of the instrument itself.
The _second_ teaches the practical working of it.
The _third_ shall contain tables of latitudes and longitudes of fixed
stars, declinations of the sun, and the longitudes of certain towns.
The _fourth_ shall shew the motions of the heavenly bodies, and especially
of the moon.
The _fifth_ shall teach a great part of the general rules of astronomical
theory.
Here begins the _first_ part; i.e. the description of the Astrolabe itself.
1. _The Ring._ See figs. 1 and 2. The Latin name is _Armilla suspensoria_;
the Arabic name is spelt _alhahuacia_ in MS. Camb. Univ. Ii. 3. 3, but
Stöffler says it is _Alanthica_, _Alphantia_, or _Abalhantica_. For the
meaning of 'rewle,' see § 13.
2. _The Turet._ This answers nearly to what we call an _eye_ or a _swivel_.
The metal plate, |